962 ; REPORT—1890. 
\Tonspersquare| « @ | & 
Original Original inch 38 are 
No. Description Size of piece JANG) ae S| BE 
in feet in feet | Elastic] Total | 3S | 2° 
limit | stress} & x n 
96 | round . 3 . | 0°75 dia. 0-441 | 158 | 246] 56 26 
97 gplate . é 4 1:00 x 0°63 0°630 16:0 | 27:9 58 29 
98 | 2 round . A . | 0°550 dia. 0-238 | 15:6 | 27:4] 65 19 
99 z round . 2 5 0°850 dia. 0°567 15:9 | 24:9 69 29 
100 #round . A é 0'850 dia. 0:567 15:7 | 23°6 71 32 
5. Measurement of Elongation in Test Samples. By J. H. WickstE£ep. 
When a bar of metal is stretched with a longitudinal pull, it first extends 
generally throughout the whole of its free length; after which, especially in best 
iron, mild steel, and copper, it extends locally about the place of final fracture. 
The ‘ general’ extension continues so long as the bar offers increasing resistance to 
the pull, and from the end of that stage to final fracture the extension is local. 
The general extension is unaffected by the shape or proportions of the specimen, 
and may be correctly expressed in units of its own length. 
The local extension bears no relation to the length of the specimen, and should, 
therefore, be expressed in standard units of length. 
The usual engineering practice of the present day is to measure the total exten- 
sion, and to express it in percentage of the original length of specimen; but this 
practice makes it difficult to draw correct comparisons of ductility between different 
experiments, unless the specimens have been all made to the same pattern. It also 
prevents the value of the material being discriminated as between capability for 
stricture and the capability for stretching without loss of strength. 
The author describes a method for separating the measurement of the general 
extension from the local, and recommends a column in test reports of ‘% general 
extension, leaving the present column of ‘% contraction of area’ to record the 
capacity for stricture, and the present column of total extension in inches, from 
which the local extension can be deduced by subtracting the recorded general 
extension from the total as measured after the sample is broken. 
6. On the Measurement of Strains. By A. Mattock. 
7. Exhibition of a Mechanism. 
By Professors Barr and W. Srrovp. 
